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A063037 Numbers without 3 consecutive equal binary digits. 10
0, 1, 2, 3, 4, 5, 6, 9, 10, 11, 12, 13, 18, 19, 20, 21, 22, 25, 26, 27, 36, 37, 38, 41, 42, 43, 44, 45, 50, 51, 52, 53, 54, 73, 74, 75, 76, 77, 82, 83, 84, 85, 86, 89, 90, 91, 100, 101, 102, 105, 106, 107, 108, 109, 146, 147, 148, 149, 150, 153, 154, 155, 164, 165, 166 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,3

COMMENTS

Complement of A136037; intersection of A003796 and A003726. - Reinhard Zumkeller, Dec 11 2007

From Emeric Deutsch, Jan 27 2018: (Start)

Also 0 together with the indices of the compositions that have no parts larger than 2. For the definition of the index of a composition see A298644.

For example, 105 is in the sequence since its binary form is 1101001 and the composition [2,1,1,2,1] has no parts larger than 2.

On the other hand, 132 is not in the sequence since its binary form is 10000100 and the composition [1,4,1,2] has a part larger than 2.

The command c(n) from the Maple program yields the composition having index n. (End)

LINKS

R. Zumkeller, Table of n, a(n) for n = 1..10000

FORMULA

It appears (but has not yet been proved) that the terms of {a(n)} can be computed recursively as follows. Let {c(i)} be defined for i >= 4 by c(i) = 2c(i-1) + 1, if n is a multiple of 3, else c(i) = 2c(i-1) - 1, with c(4) = 1. I.e., {c(i)} = {1,1,3,5,9,19,37,73,147,...}, for i=4,5,6,... . Let a(1)=1, a(2)=2, a(3)=3. For n > 3, choose k so that F(k)-2 < n <= F(k+1)-2, where F(k) denotes the k-th Fibonacci number (A000045). Then a(n) = c(k) + 2a(F(k)-2) - a(2F(k)-n-3). This has been verified for n up to 1100. - John W. Layman, May 26 2009

EXAMPLE

The binary representation of 9 (1001) has no 3 consecutive equal digits.

MAPLE

isA063037 := proc(n)

    local bdgs, rep, d, i ;

    if n = 0 then

        return true;

    end if;

    bdgs := convert(n, base, 2) ;

    rep := 1;

    d := op(1, bdgs) ;

    for i from 2 to nops(bdgs) do

        if op(i, bdgs) = op(i-1, bdgs) then

            rep := rep+1 ;

        else

            rep :=1 ;

        end if ;

        if rep > 2 then

            return false;

        end if;

    end do:

    return true ;

end proc:

for n from 0 to 50 do

    if isA063037(n) then

        printf("%d, ", n) ;

    end if;

end do: # R. J. Mathar, Dec 18 2013

# Second Maple program:

Runs := proc (L) local j, r, i, k: j := 1: r[j] := L[1]: for i from 2 to nops(L) do if L[i] = L[i-1] then r[j] := r[j], L[i] else j := j+1: r[j] := L[i] end if end do: [seq([r[k]], k = 1 .. j)] end proc: RunLengths := proc (L) map(nops, Runs(L)) end proc: c := proc (n) ListTools:-Reverse(convert(n, base, 2)): RunLengths(%) end proc: A := {0}: for n to 250 do if `subset`(convert(c(n), set), {1, 2}) then A := `union`(A, {n}) else end if end do: A; # most of this Maple program is due to W. Edwin Clark. - Emeric Deutsch, Jan 27 2018

MATHEMATICA

Select[Range[0, 168], AllTrue[Length /@ Split@ IntegerDigits[#, 2], # < 3 &] &] (* Michael De Vlieger, Aug 20 2017 *)

PROG

(PARI) { n=0; for (m=0, 10^9, x=m; t=1; b=2; while (x>0, d=x-2*(x\2); x\=2; if (d==b, c++; if (c==3, t=x=0), b=d; c=1)); if (t, write("b063037.txt", n++, " ", m); if (n==1000, break)) ) } \\ Harry J. Smith, Aug 16 2009

CROSSREFS

Cf. A000045, A000975, A286262.

Sequence in context: A032878 A032845 A023776 * A286262 A201992 A236562

Adjacent sequences:  A063034 A063035 A063036 * A063038 A063039 A063040

KEYWORD

easy,nonn

AUTHOR

Lior Manor, Jul 05 2001

EXTENSIONS

Missing "less than" sign supplied in the conjectured recurrence (thanks to Franklin T. Adams-Watters for pointing this out) by John W. Layman, Nov 09 2009

STATUS

approved

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Last modified February 21 23:27 EST 2019. Contains 320381 sequences. (Running on oeis4.)